1. Field of the Invention
The present invention relates to a computer graphics display system in which the individual viewports or images produced on a video screen are of arbitrary arrangement, number, size and content.
2. Description of the Prior Art
Especially in computer-aided design (CAD) applications, it is desirable often to have two or more views of the same or related objects displayed simultaneously on the video display screen. An example is in the CAD design of chemical process plants, where thousands of pipes, valves, fittings and equipment interconnections must be integrated into a unitary system. A design engineer would benefit from having a graphics work station at which he could simultaneously display e.g., a plan or elevation view of a major portion of the plant, an enlarged perspective view of the immediate portion of the plant piping which is undergoing design, and pictorial or schematic views of the components that the engineer is now assembling into the system. An overall objective of the present invention is to provide such a graphics display system.
A highly desirable feature of such system is the arbitary number, size and location of such simultaneous images or "viewports" on the video display screen. Thus in the example of process piping design, an engineer may prefer to have totally different sets of views available when performing design tasks on correspondingly different sections of the process plant. A further object of the present invention is to provide a graphics display system in which the viewport arrangement is completely arbitrary.
Advantageously, the image content of each viewport should be selectable independently of the contents of the other viewports. On the other hand, the system should be sufficiently flexible to allow simultaneous display of the same graphics data in two or more viewports, for example, with different magnification ("zoom") factors. Advantageously, the system should be capable of inserting a background grid over any or all of the images, with arbitrary grid spacing that can be scaled in accordance with the image magnification factor. Corresponding cursor placement in two or more images of the same data also is desirable. A further object of the present invention is to provide a graphics display system having these capabilities.
The ability to pan across a stored graphics picture also is a desirable feature. Advantageously, the display system should permit independent panning in any of the simultaneously displayed viewports. This is another objective of the present invention.
Certain techniques for implementing zoom, panning and split screen display effects are disclosed in the inventors' U.S. Pat. No. 4,197,590 entitled METHOD FOR DYNAMICALLY VIEWING IMAGE ELEMENT STORED IN A RANDOM ACCESS MEMORY ARRAY, and in the corresponding RASTER SCAN DISPLAY APPARATUS U.S. Pat. No. 4,070,710 now reissued as U.S. Pat. No. RE31,200. An objective of the present invention is to provide a graphics display system having a technique for viewport allocation and content which is different from, and more flexible than that disclosed in the inventors' referenced patents. On the other hand, certain features such as the pan and zoom techniques disclosed in those referenced patents advantageously may be incorporated with the present invention. Two other features which likewise may be incorporated with the present invention are background grid generation and toroidal panning. These techniques are disclosed in the inventors' U.S. Pat. No. 4,295,135 entitled "ALIGNABLE ELECTRONIC BACKGROUND GRID GENERATION SYSTEM" and application Ser. No. 274,355 now U.S. Pat. No. 4,442,495 entitled "TOROIDAL PAN". A further object of the present invention is to provide a graphics display system in which such zoom, pan, background grid and toroidal panning capabilities can be implemented independently and simultaneously in a plurality of viewports of arbitrary size and location.